Recovering part of the energy that was let go in form of waste heat via a thermoelectric power generator is drawing more and more interests from the automobile industry as well as many other areas. Mass production of bulk materials with high figure of merit zT, defined as zT=S2T/ρκ (S is the Seebeck coefficient, ρ is the electric resistivity and κ is the thermal conductivity), is the key to promoting wide application of such thermoelectric devices. During the past decades materials scientists have been searching for good thermoelectric candidates among semiconductors that have adequate band gaps as well as low thermal conductivities. However, there is still a need in the art for improved thermoelectric materials.